Body mass index is a measure of body fat based on your weight in relation to your height. BMI percentile is the best assessment of body fat. Lifestyle practices are considered to be the important determinant of health and sickness. In our study lifestyle practices include physical activity and dietary practices. The objectives of the study were to calculate the BMI of adolescents, to assess the lifestyle practices of adolescents and to find out the association of BMI and lifestyle practices of adolescents. A quantitative descriptive study was carried out in selected villages of District Sirmour, (HP), using non-probability convenience sampling, 60 adolescents between the age group of 13-19 years were selected from selected areas. Subjects were interviewed using structured questionnaire regarding demographic variables and checklist for the lifestyle practices which were followed by adolescents. Data was analysed by manually in terms of descriptive and inferential statistics. The result shows that more than half of the samples were having normal BMI i.e. 34(56.66%), 24(40%) adolescents come under the underweight category, only 2 (3.33%) adolescents come under overweight category and out of 60 samples no one come under obese category. 42(70%) samples have normal good practices, 11(18.33%) were having very good practices, only 7(11.66%)having fair practices and 0(0%) out of 60 samples having poor practices. By applying Chi square method the level of significance of association of BMI and lifestyle practices is (p=0.05). In conclusion, we as nurses must continue to remind and update the community adolescents about good lifestyle practices and early identification of cases of malnutrition and obesity. Intensive educational campaigns to increase awareness regarding good lifestyle practices in order to increase awareness regarding malnutrition and obesity.